CN - Chapter 2 - Neurons and Glia

Question 1

glial cell

Answer 1

A support cell in the nervous system. Glia are classified into four categories:

• astrocytes
• oligodendroglia
• Schwann cells
• microglia

Astrocytes regulate the extracellular environment of the brain, oligodendroglia and Schwann cells provide myelin, and microglia scavenge debris.

Question 2

neuron

Answer 2

The information processing cell of the nervous system; also called a nerve cell. Most neurons use action potentials to send signals over a distance, and all neurons communicate with one another using synaptic transmission.

Question 3

histology

Answer 3

The microscopic study of the structure of tissues.

Question 4

Nissl stain

Answer 4

A class of basic dyes that stain the somata of neurons;

named for its disoverer, German histologist Franz Nissl (1860-1919).

Question 5

cytoarchitecture

Answer 5

The arrangement of neuronal cell bodies in various parts of the brain.

Question 6

Golgi stain

Answer 6

A method of staining brain tissue that shows neurons and all of their neurites;

named for its disoverer, Italian histologist Camillo Golgi (1843-1926).

Question 7

cell body / soma / perikaryon

Answer 7

The central region of the neuron containing the nucleus.

Question 8

neurite

Answer 8

A thin tube extending from a neuronal cell body;

the two types are axons and dendrites.

Question 9

axon

Answer 9

A neurite specialized to conduct nerve impulses, or action potentials, normally away from the soma.

Question 10

dendrite

Answer 10

A neurite specialized to receive snyaptic inputs from other neurons.

Question 11

neuron doctrine

Answer 11

The concept that the neuron is the elementrary functional unit of the brain and that neurons communicate with each other by contact, not continuity.

Question 12

cytosol

Answer 12

The watery fluid inside a cell.

Question 13

organelle

Answer 13

A membrane-enclosed structure inside a cell;

examples are the nucleus, mitochondrion, endoplasmic reticulum, and Gogi apparatus.

Question 14

cytoplasm

Answer 14

Cellular material contained by the cell membrane, including the organelles but excluding the nucleus.

Question 15

nucleus

Answer 15

1. The roughly spherical organelle in a cell body containing the chromosomes.
2. A clearly distinguishable mass of neurons, usually deep in the brain.

Question 16

chromosome

Answer 16

A structure in the cell nucleus containing a single linear thread of DNA.

Question 17

DNA (deoxyribonucleic acid)

Answer 17

A double-stranded molecule constructed from four nucleic acids that contains the genetic instructions for a cell.

Question 18

gene

Answer 18

A unit of heredity;

a sequence of DNA that encodes a single polypeptide or protein.

Question 19

gene expression

Answer 19

The process of transcribing the information from a gene into messenger RNA (mRNA);

a gene is a segment of DNA carrying the instructions for a single protein (or polypeptide).

Question 20

protein

Answer 20

A polymer of amino acids strung together by peptide bonds.

Question 21

protein synthesis

Answer 21

The assembly of protein molecules in the cell’s cytoplasm according to genetic instructions.

Question 22

mRNA (messenger ribonucleic acid)

Answer 22

A molecule constructed from four nucleic acids that carries the genetic instructions for the assembly of a protein from the nucleus to the cytoplasm.

Question 23

transcription

Answer 23

The process of synthesizing a messenger RNA molecule according to genetic instructions encoded in DNA.

Question 24

promoter

Answer 24

A region of DNA that binds RNA polymerase to initiate gene transcription.

Question 25

transcription factor

Answer 25

A protein that regulates the binding of RNA polymerase to a gene promoter.

Question 26

RNA splicing

Answer 26

The process by which introns, the regions of a primary RNA transcript that are not used to code protein, are removed.

Question 27

amino acid

Answer 27

A chemical building block of protein molecules, containing a central carbon atom, an amino group, a carboxyl group, and a variable R group.

Question 28

translation

Answer 28

The process of synthesizing a protein molecule according to genetic instructions carried by a messenger RNA molecule.

Question 29

ribosome

Answer 29

A cellular organelle that assembles new proteins from amino acids according to the instructions carred by messenger RNA.

Question 30

rough endoplasmic reticulum (rough ER)

Answer 30

A membrane-enclosed cellular organelle with robosomes attached to its outer surface; a site of synthesis for proteins destined to be inserted into membrane or to be enclosed by membrane.

Question 31

polyribosome

Answer 31

A collection of several ribosomes floating freely in the cytoplasm.

Question 32

smooth endoplasmic reticulum (smooth ER)

Answer 32

A membrane-enclosed organelle that is heterogeneous and performs different functions in different locations.

Question 33

Golgi apparatus

Answer 33

An organelle that sorts aand chemically modifies proteins that are destined for delivery to different parts of the cell.

Question 34

mitochondrion

Answer 34

An organelle responsible for cellular respiration. Mitochondria generate adenosine triphosphate (ATP) using the energy produced by the oxidation of food.

Question 35

ATP (adenosine triphosphate)

Answer 35

The molecule that is the cell's energy source. The hydrolysis of ATP to produce adenosine diphosphate (ADP) releases energy that fuels most of the biochemical reactions of the neuron. ADP is converted back to ATP in the mitochondria.

Question 36

neuronal membrane

Answer 36

The barrier, about 5 nm thick, that separates the inside of a nerve cell from the outside; consists of a phospholipid bilayer with proteins embedded in it; encloses the intracellular organelles and vesicles.

Question 37

cytoskeleton

Answer 37

The internal scaffolding that gives a cell its characteristic shape; consists of **microtubules**, **neurofilaments**, and **microfilaments**.

Question 38

microtubule

Answer 38

A polymer of the protein tubulin, forming a straight, hollow tube 20 nm in diameter. Microtubules, a component of the cytoskeleton, play an important role in axoplasmic transport.

Question 39

microfilament

Answer 39

A polymer of the protein actin, forming a braided strand 5 nm in diameter; a component of the cytoskeleton.

Question 40

neurofilament

Answer 40

A type of intermediate filament found only in neurons, 10 nm in diameter; an important component of the neuronal cytoskeleton.

Question 41

axon hillock

Answer 41

A swelling of the axon where it joins the soma.

Question 42

axon collateral

Answer 42

A branch of an axon.

Question 43

axon terminal

Answer 43

The end region of an axon, usually a site of synaptic contact with another cell; also called terminal bouton or presynaptic terminal.

Question 44

terminal bouton

Answer 44

The end region of an axon; usually a site of synaptic contact with another cell; also called an axon terminal.

Question 45

synapse

Answer 45

The region of contact where a neuron transfers information to another cell.

Question 46

terminal arbor

Answer 46

Branches at the end of an axon terminating in the same region of the nervous system.

Question 47

innervation

Answer 47

The provision of a synaptic input to a cell or collection of cells.

Question 48

synaptic vesicle

Answer 48

A membrane-enclosed structure, about 50 nm in diameter, containing a neurotransmitter and found at a site of synaptic contact.

Question 49

synaptic cleft

Answer 49

The region separating the presynaptic and post synaptic membranes of neurons.

Question 50

synaptic transmission

Answer 50

The process of transferring information from one cell to another at a synapse.

Question 51

neurotransmitter

Answer 51

A chemical released by a presynaptic element upon stimulation that activates postsynaptic receptors.

Question 52

axoplasmic transport

Answer 52

The process of transporting materials down an axon.

Question 53

anterograde transport

Answer 53

Axoplasmic transport from a neuron's soma to the axon terminal.

Question 54

retrograde transport

Answer 54

Axoplasmic transport from an axon terminal to the soma.

Question 55

dendritic tree

Answer 55

All the dendrites of a single neuron.

Question 56

receptor

Answer 56

1. A specialized protein that detects chemical signals, such as neurotransmitters, and initiates a cellular response. 2. A specialized cell that detects environmental stimuli and generates neural responses.

Question 57

dendritic spine

Answer 57

A small sac of membrane that protrudes from the dendrites of some cells and recieves synaptic input.

Question 58

unipolar neuron

Answer 58

A neuron with a single neurite.

Question 59

bipolar neuron

Answer 59

A neuron with two neurites.

Question 60

multipolar neuron

Answer 60

A neuron with three or more neurites.

Question 61

stellate cell

Answer 61

A neuron characterized by a radial, star-like distribution of dendrites.

Question 62

pyramidal cell

Answer 62

A neuron characterized by a pyramid-shaped cell body and elongated dendritic tree; found in the cerebral cortex.

Question 63

spiny neuron

Answer 63

A neuron with dendritic spines.

Question 64

aspinous neuron

Answer 64

A neuron lacking dendritic spines.

Question 65

primary sensory neuron

Answer 65

A neuron specialized to detect environmental signals at the body's sensory surfaces.

Question 66

motor neuron

Answer 66

A neuron that synapses on a muscle cell and causes muscle contraction.

Question 67

interneuron

Answer 67

Any neuron that is not a sensory or motor neuron; also describes a CNS neuron whose axon does not leave the structure in which it resides.

Question 68

astrocyte

Answer 68

A glial cell in the brain that supports neurons and regulates the extracellular ionic and chemical environment.

Question 69

oligodendroglial cell

Answer 69

A glial cell that provies myelin in the central nervous system.

Question 70

Schwann cell

Answer 70

A glial cell that provides myelin in the peripheral nervous system.

Question 71

myelin

Answer 71

A membranous wrapping, or sheath, around axons, provided by **oligodendroglia** in the CNS and **Schwann cells** in the peripheral nervous system.

Question 72

node of Ranvier

Answer 72

A space between two consecutive myelin sheaths where an axon comes in contact with the extracellular fluid.

Question 73

ependymal cell

Answer 73

A type of glial cell that provides the lining of the brain's ventricular system.

Question 74

microglial cell

Answer 74

A type of cell that functions as a phagocyte in the nervous system to remove debris left by dead or dying neurons and glia.

Question 75

What are two factors that distinguish the axon from the soma?

Answer 75

1. No rough ER extends into the axon, and there are few, if any, free ribosomes. 2. The protein composition of the axon membrane is fundamentally different from that of the soma membrane.

Question 76

How does the cytoplasm of the axon terminal differ from that of the axon?

Answer 76

1. Microtubules do not extend into the terminal. 2. The terminal contains numerous small bubbles of membrane, called *synaptic vessicles*, that measure about 50 nm in diameter. 3. The inside surface of the membrane that faces the synapse has a particularly dense covering of proteins. 4. It has numerous mitochondria, indicating a high energy demand.

Question 77

State the neuron doctrine in a single sentence. To whom is this insight credited?

Answer 77

The neuron doctrine is the idea that the neurons are not continuous with one another but are *discrete cells that communicate by contact and not by continuity*. This insight is credited to Santiago Ramón y Cajal.

Question 78

Which parts of a neuron are shown by a Golgi stain that are not shown by a Nissl stain?

Answer 78

The Golgi stain shows the neuronal cell body with the dendrites and the axon. The Nissl stain shows only the cell body.

Question 79

What are the three physical characteristics that distinguish axons from dendrites?

Answer 79

The three physical characteristics that distinguish axons from dendrites are: **i)** The cell body usually gives rise to a single axon while many dendrites extend from the cell body. **ii)** The axon is of uniform diameter throughout its length while dendrites rarely extend more than 2 mm in length. **iii)** The branches of an axon generally extend at right angles while dendrites generally taper to a fine point.

Question 80

Among the following structures, state those which are unique to neurons and the ones that are not: nucleus, mitochondria, rough ER, synaptic vesicle, and Golgi apparatus.

Answer 80

The synaptic vesicle is unique to neurons whereas the nucleus, the mitochondria, the rough ER, and Golgi apparatus are not unique to neurons.

Question 81

What are the steps by which the information in the DNA of the nucleus directs the synthesis of a membrane-associated protein molecule?

Answer 81

Protein synthesis occurs in the cytoplasm; DNA never leaves the nucleus. To transport the information necessary for protein synthesis, mRNA is used... The process of assembling a piece of mRNA that contains the information of a gene is called transcription and the resulting mRNA is called the transcript... Amino acids are brought to the ribosome by transfer RNA (tRNA). The assembling of proteins from amino acids under the direction of the mRNA is called translation.

Question 82

Colchicine is a drug that causes microtubules to break apart or depolymerize. What effect would this drug have on anterograde transport? What would happen in the axon terminal?

Answer 82

Vesicles containing molecules needed at the axon terminal "walk down" the microtubules within the axon on "legs" provided by a protein called kinesin. The process is fueled by ATP. Kinesin moves material only from the soma to the terminal. Movement in this direction is called anterograde transport. The application of colchicines causes microtubules to disintegrate, and when applied to the axon disrupts the path for anterograde transport. As a result, all movement of material from the soma to the terminal (anterograde transport) ceases. If the colchicines application does not kill the whole cell, then the material to be transported will accumulate on the side of the axon closest to the soma.

Question 83

Classify the cortical pyramidal cell based on (a) the number of neurites, (b) the presence or absence of dendritic spines, (c) connections, and (d) axon length.

Answer 83

Classification of the cortical pyramidal cell is as follows: (a) Cortical pyramidal cells have three or more neurites and are multipolar. (b) Cortical pyramidal cells have dendritic spines. (c) Axons of cortical pyramidal cells project to other cortical areas and also to several subcortical areas as well. (d) In the cerebral cortex, pyramidal cells usually have long axons that extend to other parts of the brain and are therefore Golgi type I neurons.

Question 84

What is myelin and what does it do? Which cells provide myelin to the central nervous system?

Answer 84

Myelin refers to layers of glial membrane that insulate axons. Myelin speeds the propagation of nerve impulses down the axon. The oligodendroglial cells provide myelin in the central nervous system. (Schwann cells provide myelin in the peripheral nervous system.)